The present invention relates to compositions which are highly effective as herbicidal formulations. The compositions are composed of an aqueous solution of an ammonium salt of a carboxylic acid and a dicarboxylic acid diester.
Persistent plants that interfere with the growth of desirable plants, such as food crops, ornamentals, turf grass, etc. are known as weeds. For economic and other reasons, mankind has been trying to control the growth of weeds since agriculture first began. One means of weed control has been by the use of chemicals known as herbicides. The sale of herbicides worldwide is in the billions of dollars per year.
There are two major categories of herbicidesxe2x80x94selective and non-selective. Selective herbicides only kill selected weeds such as broad leafed plants like dandelion. Exemplary of well-known herbicides is 2,4-D. Non-selective herbicides kill all weeds. Commercially known non-selective herbicides include glyphosate (such as ROUNDUP(copyright)) and paraquat. Many of the selective and non-selective herbicides of the prior art are highly toxic. For example, paraquat is a known hazardous material and ROUNDUP often has a higher than desired kill time.
Further, many herbicides, regardless of whether they are selective or non-selective, are toxic to mammals, present complications resulting from buildup in the soil or have other properties which are of concern to health and environmental authorities. Researchers are constantly aiming to overcome some of these concerns.
Recently, it was shown in U.S. Pat. No. 6,323,156, issued on Nov. 27, 2001, that water solutions of ammonium fatty acid salts, such as ammonium pelargonate, function effectively as a non-selective herbicide. Since ammonium pelargonate is derived from naturally occurring pelargonic acid (nonanoic acid) and is non-toxic and biodegradable, it has desirable properties from a safety and environmental standpoint along with its ability to kill weeds. Although being a non-selective herbicide, it is not capable of destroying all weeds.
Further, dimethyl esters of naturally occurring dibasic acids such as azelaic acid, suberic acid and sebacic acid are known to function as non-selective herbicides. These compounds are further non-toxic and biodegradable. Furthermore, they are able to control some weeds that ammonium salts of fatty acids do not. However, since they are completely water insoluble, they are often commercially impractical. For instance, the preparation of a water solution of dimethyl azelate for herbicidal applications requires the use of large amounts of water soluble organic liquids such as acetone or ethanol. In addition to being impractical, such compositions, in light of the water insolubility of the diacid ester, are expensive. Often, such diesters must be applied to the target weed as an emulsion (using inactive emulsifying agents) or as a dispersion (using wettable powders by mixing them with clay). As such, these compositions are more cost prohibitive and less desirable than a water solution. Non-toxic biodegradable herbicides compatible in a water-based formulation are therefore desired.
Aqueous compositions containing ammonium salts of fatty acids and dicarboxylic acid diesters function remarkably as non-selective herbicides. In the compositions of the invention, the diester of a carboxylic diacid is solubilized in a water solution containing the ammonium salt of a fatty acid, such as ammonium pelargonate. The resulting composition can be diluted with water to render a stable emulsion which may be applied to the locus of unwanted vegetation. Since the mode of action is through the leaves of the vegetation, there is little, if any, residual herbicidal effect in the ground. Thus, it is possible to grow desirable plants adjacent to and around the treated area.
The ammonium salt is a compound of the formula:
R1 COOxe2x88x92X+xe2x80x83xe2x80x83(I) 
wherein R1 is a C7 to C11 hydrocarbyl group and X is ammonium (NH4+). In the formula (I), any of the hydrogen on R1 may be substituted with one or more hydroxyl or a C1-C5 hydrocarbyl group, such as an alkyl group. In a preferred embodiment, the compound of formula (I) is ammonium pelargonate.
Suitable as the dialkyl ester of the dicarboxylic acid are those diesters of the formula:
ROOC(CHR2)nCOORxe2x80x2xe2x80x83xe2x80x83(II) 
wherein R and Rxe2x80x2 are independently selected from a C1 to C8 alkyl group, R2 is hydrogen or a C1-C3 alkyl group, and n is from 2 to 10. R and Rxe2x80x2 on any given compound may be the same or different alkyl group. Highly preferred are those diesters wherein R and Rxe2x80x2 are the same alkyl group. Particularly desirable esters are the dimethyl esters wherein n is 6 to 8, such as the dimethyl ester of azelaic acid.